Two rods A and B of different materials are welded together as shown in figure. Their thermal conductivities are `K_(1)` and `K_(2)`. The thermal conductivity of the composite rod will be

Options

A. `(3(K_(1) + K_(2)))/(2)`
B. `K_(1) + K_(2)`
C. `2 (K_(1) + K_(2))`
D. `(K_(1) + k_(2))/(2)`

Explanation

`(1)/(R_(eq)) = (1)/(R_(1)) + (1)/(R_(2))`
`(K_(eq) . 2 A)/(L) = (K_(1) A)/(L) + (K_(2) A)/(L)`
` K_(eq) = (K_(1) + K_(2))/(2)`